This invention relates to coating substrates, particularly glass substrates, with coatings comprised primarily of metal oxides. This invention more particularly relates to contacting a hot glass surface with the vapors of reactants which form metal oxide coatings upon contacting the hot glass surface.
Prior to the present invention it has been known that substrates may be coated with metal oxide coatings by contacting the substrates with solutions comprised of metal betadiketonates and the like dissolved in appropriate solvents. See the following U.S. Patents: Mochel, U.S. Pat. No. 3,202,054, Tompkins, U.S. Pat. No. 3,081,200, Donley et al, U.S. Pat. No. 3,660,061 and Michelotti et al. U.S. Pat. No. 3,652,246. These patents have disclosed to the public a number of chemical compositions which are suitable for the coating of glass with metal oxide coatings. In general, the techniques described for applying such coatings to glass taught in the prior art are methods wherein a liquid spray of coating composition is directed against a glass substrate surface to be coated. While these patents cover the application of particular metals or metal oxides to glass or other substrates, whether the compositions are applied in liquid or vapor form, they each disclose, as a best mode of application, contacting the substrate with the compositions in liquid form. In the development of techniques for applying vaporized coating compositions to heated substrates at atmospheric pressure certain difficulties have been encountered. It has been difficult to obtain coatings which are finely grained and uniform in appearance. Thick coatings have been produced by contacting the substrate with a liquid spray, but it has been extremely difficult, if not impossible, to obtain relatively thick films having visible light transmittances of below about 50% using known vapor deposition techniques.
Vapor deposition processes have been known in the past. Most commercial embodiments of vapor deposition processes are processes carried out under subatmospheric pressure conditions. A number of techniques have evolved for enhancing the rate of film deposition using these techniques, for example, electrical fields, magnetic fields, and radio frequency or microwave excitation have been used to increase the momentum of reaction particles in vapor coating compositions during their applications. Also, wave guides have been used to direct the vapors of coating compositions to particularly confined target areas. See U.S. Pat. No. 3,114,652 to Schetky and U.S. Pat. No. 3,561,940 to Scholes.
The applicant has now discovered that the uniformity of films produced by chemical vapor deposition and the rate of chemical vapor deposition or film buildup may be significantly enhanced by employing nozzles of particular design, particularly when used in combination with particular flow conditions and nozzle-to-substrate spacings.